1a chivalrous, courteous, or honourable man:he behaved throughout like a perfect gentleman
a man of good social position, especially one of wealth and leisure.
a man of noble birth attached to a royal household:a Gentleman of the Bedchamber
2a polite or formal way of referring to a man:opposite her an old gentleman sat readingcan I help you, gentlemen?
used as a courteous title for a male fellow member of the House of Commons or the House of Representatives:the Right Honourable Gentleman opposite
Middle English (in the sense 'man of noble birth'): from gentle1+ man, translating Old French gentilz hom. In later use the term denoted a man of a good family (especially one entitled to a coat of arms) but not of the nobility
gentleman in other Oxford dictionaries
Definition of gentleman in the US English dictionary